In addition to flash memories, ferroelectric memories such as FeRAM (Ferroelectric Random Access Memory) are well-known as nonvolatile memories capable of retaining stored information even after a power supply is turned off.
A ferroelectric memory includes a capacitor using a ferroelectric film as a capacitor dielectric film. Information is stored in the ferroelectric memory with the direction of the polarity of the ferroelectric film caused to correspond to “1” or “0”. There is an advantage in that the ferroelectric memory is capable of operating at low power consumption and at high speed as compared with the flash memory.
In many cases, an oxide ferroelectric such as PZT (Lead Zirconium Titanate) is used as a material for the ferroelectric film.
However, the oxide ferroelectrics are easily reduced by a reductant such as water and hydrogen to greatly deteriorate ferroelectric characteristics such as a switching charge. To protect a capacitor from such a reductant, there is a proposed structure in which a capacitor is covered with a protection film such as an alumina film to prevent a reductant from intruding into the capacitor.
Note that the related techniques are disclosed in Japanese Laid-open Patent Publications No. 2005-183843, No. 2005-327847, No. 2008-84880, and No. 2009-105084.